In a transmission system for displaying image information on, for example, an original image acquired by a camera, the temporarily encoded and compressed original image is transmitted and then a decoded image obtained by decoding is displayed. Generally, an enormous amount of image information is transmitted and thus transmission bandwidths need to be reduced in transmission paths such as a network. Such an image transmission system may require image recognition instead of or in addition to display. For example, image recognition is required to detect a suspect using a monitoring camera, identify a distance between vehicles and a road sign using an on-board camera, or avoid a collision between a pedestrian and another vehicle or another obstacle.
Japanese Unexamined Patent Publication No. 2013-239995 discloses an on-board camera system that recognizes images using compressed and expanded pictures to assist driving of vehicles. Depending on the running condition of a vehicle and a driving assistance application (e.g., a lane passing alarm, collision avoidance, and rear moving image display), encoding control information including an image size in a moving image format, a color format, a frame rate, and a bit depth is transmitted to the encoder control unit of a moving image transmitter, a sender changes an encoding parameter based on the encoding control information, and then a moving image stream is generated.
Japanese Unexamined Patent Publication No. 2008-22404 discloses an image encoding device that includes a feature quantity extracting unit upstream of image encoding, calculates the flatness (activity) of an image in a feature quantity calculating unit, and improving image quality by determining a parameter for a deblocking filter included in image encoding.